Image processing apparatus that generates evaluation value for evaluating luminance of image data, image capturing apparatus, method for processing image, and program

Abstract

An apparatus includes a band limiting circuit, a reducing circuit, a correcting circuit, and an evaluation-value generating circuit. The band limiting circuit is configured to perform a band limiting process on image data. The reducing circuit is configured to reduce the image data to generate reduced image data. The correcting circuit is configured to perform a correcting process corresponding to the attenuation rate of the band limiting process on a signal level obtained from the reduced image data. The evaluation-value generating circuit is configured to generate an evaluation value indicating the luminance of the image data based on the image data.

What is claimed is: 
     
         1 . An apparatus comprising:
 at least one memory device;   at least one processor;   a band limiting unit configured to perform a band limiting process on image data;   a reducing unit configured to reduce the image data to generate reduced image data;   a correcting unit configured to perform a correcting process corresponding to an attenuation rate of the band limiting process on a signal level obtained from the reduced image data; and   an evaluation-value generating unit configured to generate an evaluation value indicating luminance of the image data based on the image data,   wherein the band limiting unit, the reducing unit, the correcting unit, and the evaluation-value generating unit are implemented by the at least one processor executing at least one program stored in the at least one memory device.   
     
     
         2 . The apparatus according to  claim 1 ,
 wherein the correcting unit separates the reduced image data into frequency components and corrects a signal level of each frequency component according to an attenuation rate corresponding to each frequency component.   
     
     
         3 . The apparatus according to  claim 2 ,
 wherein the correcting unit applies a gain corresponding to each frequency component to the signal level of each frequency component and sets the gain so as not to exceed a predetermined value.   
     
     
         4 . The apparatus according to  claim 2 ,
 wherein the correcting unit separates the reduced image data into frequency components by applying a Fourier transform on the reduced image data.   
     
     
         5 . The apparatus according to  claim 4 ,
 wherein the correcting unit applies an inverse Fourier transform to the frequency component corrected according to the attenuation rate corresponding to each frequency component.   
     
     
         6 . The apparatus according to  claim 1 ,
 wherein the correcting unit counts continuous pixels whose signal levels are higher than a threshold in the reduced image data and performs a correcting process according to the attenuation rate of the band limiting process based on the count.   
     
     
         7 . The apparatus according to  claim 6 ,
 wherein the correcting unit determines a gain to be applied to the signal level of a pixel in the counted area based on the count.   
     
     
         8 . An apparatus comprising:
 at least one memory device;   at least one processor;   a band limiting unit configured to perform a band limiting process on image data;   a reducing unit configured to perform a reduction process on the image data to generate reduced image data;   a determination unit configured to determine whether each area in the reduced image data satisfies a predetermined condition; and   an evaluation-value generating unit configured to, for an area that is determined to satisfy the predetermined condition, generate an evaluation value indicating luminance of the image data based on a signal level of the reduced image data, and for an area that is not determined to satisfy the predetermined condition, generate an evaluation value indicating the luminance of the image data based on the signal level of image data before being subjected to the band limiting process and the reduction process,   wherein the band limiting unit, the reducing unit, the determination unit, and the evaluation-value generating unit are implemented by the at least one processor executing at least one program stored in the at least one memory device.   
     
     
         9 . The apparatus according to  claim 8 ,
 wherein the determination unit counts continuous pixels whose signal levels are higher than a threshold in the reduced image data, determines whether a frequency in each area is equal to or lower than a threshold based on the count, and determines an area whose frequency is equal to or lower than the threshold as an area that satisfies the predetermined condition.   
     
     
         10 . An apparatus comprising:
 an image sensor;   at least one memory device;   at least one processor;   a control unit configured to control exposure of the image sensor;   a band limiting unit configured to perform a band limiting process on image data;   a reducing unit configured to reduce the image data to generate reduced image data;   a correcting unit configured to perform a correcting process corresponding to an attenuation rate of the band limiting process on a signal level obtained from the reduced image data; and   an evaluation-value generating unit configured to generate an evaluation value indicating luminance of the image data based on the image data,   wherein the control unit controls exposure of the image sensor based on the generated evaluation value, and   wherein the control unit, the band limiting unit, the reducing unit, the correcting unit, and the evaluation-value generating unit are implemented by the at least one processor executing at least one program stored in the at least one memory device.   
     
     
         11 . An apparatus comprising:
 an image sensor;   at least one memory device;   at least one processor;   a control unit configured to control exposure of the image sensor;   a band limiting unit configured to perform a band limiting process on image data;   a reducing unit configured to perform a reduction process on the image data to generate reduced image data;   a determination unit configured to determine whether each area in the reduced image data satisfies a predetermined condition; and   an evaluation-value generating unit configured to, for an area that is determined to satisfy the predetermined condition, generate an evaluation value indicating luminance of the image data based on a signal level of the reduced image data, and for an area that is not determined to satisfy the predetermined condition, generate an evaluation value indicating the luminance of the image data based on the signal level of image data before being subjected to the band limiting process and the reduction process,   wherein the control unit controls exposure of the image sensor based on the generated evaluation value, and   wherein the control unit, the band limiting unit, the reducing unit, the determination unit, and the evaluation-value generating unit are implemented by the at least one processor executing at least one program stored in the at least one memory device.   
     
     
         12 . A method for processing an image, the method comprising:
 performing a band limiting process on image data;   reducing the image data to generate reduced image data;   performing a correcting process corresponding to an attenuation rate of the band limiting process on a signal level obtained from the reduced image data; and   generating an evaluation value indicating luminance of the image data based on the image data.   
     
     
         13 . The method according to  claim 12 , wherein the performing the correcting process includes separating the reduced image data into frequency components and correcting a signal level of each frequency component according to an attenuation rate corresponding to each frequency component. 
     
     
         14 . The method according to  claim 12 , wherein the performing the correcting process includes counting continuous pixels whose signal levels are higher than a threshold in the reduced image data and performing a correcting process according to the attenuation rate of the band limiting process based on the count. 
     
     
         15 . A method for processing an image, the method comprising:
 performing a band limiting process on image data;   performing a reduction process on the image data to generate reduced image data;   determining whether each area in the reduced image data satisfies a predetermined condition; and   for an area that is determined to satisfy the predetermined condition, generating an evaluation value indicating luminance of the image data based on a signal level of the reduced image data, and for an area that is not determined to satisfy the predetermined condition, generating an evaluation value indicating the luminance of the image data based on the signal level of image data before being subjected to the band limiting process and the reduction process.   
     
     
         16 . The method according to  claim 15 ,
 wherein the determining includes counting continuous pixels whose signal levels are higher than a threshold in the reduced image data, determining whether a frequency in each area is equal to or lower than a threshold based on the count, and determining an area whose frequency is equal to or lower than the threshold as an area that satisfies the predetermined condition.   
     
     
         17 . A nonvolatile memory that stores a program for causing a computer of an apparatus to execute a control method, the control method comprising:
 performing a band limiting process on image data;   reducing the image data to generate reduced image data;   performing a correcting process corresponding to an attenuation rate of the band limiting process on a signal level obtained from the reduced image data; and   generating an evaluation value indicating luminance of the image data based on the image data subjected to the correcting process.   
     
     
         18 . The nonvolatile memory according to  claim 17 ,
 wherein the performing the correcting process includes separating the reduced image data into frequency components and correcting a signal level of each frequency component according to an attenuation rate corresponding to each frequency component.   
     
     
         19 . The nonvolatile memory according to  claim 17 ,
 wherein the performing the correcting process includes counting continuous pixels whose signal levels are higher than a threshold in the reduced image data and performing a correcting process according to the attenuation rate of the band limiting process based on the count.   
     
     
         20 . A nonvolatile memory that stores a program for causing a computer of an apparatus to execute a control method, the control method comprising the steps of:
 performing a band limiting process on image data;   performing a reduction process on the image data to generate reduced image data;   determining whether each area in the reduced image data satisfies a predetermined condition; and   for an area that is determined to satisfy the predetermined condition, generating an evaluation value indicating luminance of the image data based on a signal level of the reduced image data, and for an area that is not determined to satisfy the predetermined condition, generating an evaluation value indicating the luminance of the image data based on the signal level of image data before being subjected to the band limiting process and the reduction process.